Breathing process

1. Breathing control centre are:

• located in two major regions (medulla oblongata + pons).
• in medulla - sets the basic rhythm,
• in pons - moderates it smoothing out the transition between inhalation + exhalation.
• send impulses to the diaphragm + external intercostals muscle.

2. The central chemoreceptors (lies near the breathing control centers):

• detet the changes in pH of the cerebospinal fluid (CSF).
• stimulate the breathing centre
• slow down or speed the rhythmic discharge of nerve impulses

3. Carotid bodies are

• found in the carotid artery in the neck.
• chemoreceptor with nerve endings in the wall of carotid artery
• monitors the changes of blood pH in the carotid artery.

4. Aortic bodies are

• found in aorta.
• chemoreceptors that monitor the changes of blood pH.
• nerve endings in the wall of aorta.

5. Aortic and carotid bodies:

• also called peripheral chemoreceptors.
• impulses are relayed to the breathing control centres.
• change of CO2 conc. in the blood triggers a series of chain reactions.
• blood CO2 conc. back to normal,
• negative feedback loop.

6. In the blood plasma:

• CO2 released by cellular respiration 
• reacts with H2O to form carbonic acid (H2CO2)
• dissociates to form hydrogen carbonate ions (HCO3+) and hydrogen ions (H+).
• increase in hydrogen ions (H+) conc.
• increase the acidity of the blood plasma,
• decreasing the pH.

7. In the region of medulla

• CO2 diffuses into CSF from the surrounding capillary.
• then reacts with H2O in the fluid to form carbonic acid (H2CO3).
• dissociates to form hydrogen carbonate (HCO3+) and hydrogen ions (H+).
• The acidity in the CSF increases
• resulting in the decreases in the pH.

8. When blood flows through Peripheral Chemoreceptors (from aortic + carotid bodies) + Central Chemoreceptor

à detect increase in H⁺ conc

à send impulses to breathing control centre (in medulla oblongata)

à sends impulses to diaphragm + external intercostals muscles to contract faster

à breathing rate increases (to expel excess CO2)

à lungs expand (for faster breathing)

à stimulates stretch receptors (in lungs)

à send impulses to the breathing control centre

à sends impulses (via parasympathetic nerve) to the diaphragm + external intercostals muscle

à to slow down the contraction

à breathing rate returns to normal

à negative feedback reaction.